Acetabular cup positioning device

ABSTRACT

An acetabular trialing system has a trial cup including a body comprising an outer surface, a part-spherical inner surface and a rim extending between the inner and outer surface with a plurality of spaced inwardly resiliently deflectable rim members each connected at a first end to the body outer surface. The part-spherical inner surface has a plurality of spaced resilient deflectable bearing members each forming part of the body part-spherical inner surface. The bearing members have a first end deflectable towards the body outer surface. Upon inward deflection, one of the plurality of deflectable rim members is capable of contacting the first end of a corresponding one of the plurality of deflectable bearing members and moving the bearing member towards the body outer surface and into contact an electrical signaling device mounted on the body intermediate the outer surface thereof and the deflectable bearing member.

BACKGROUND OF THE INVENTION

The present invention relates generally to the alignment of anacetabular implant device in connection with the implantation of aprosthetic hip joint in a natural pelvis and pertains, morespecifically, to an apparatus and method which utilizes a disposabletrial impingement sensor to guide the appropriate alignment of theacetabular device at an implant site in the pelvis.

Many articulating joints of the body, such as the joints of the hips,have anatomical ball and socket connections between bones of the jointsproviding a wide range of motion. The hip joint, for instance, includesa socket or acetabulum in the pelvis and a femoral head or ball at anupper end of the femur or thigh bone received in the acetabulum. Wherenatural articulating joints are congenitally defective or becomedegraded due to disease or injury, prosthetic or artificial ball andsocket components are commonly implanted in the body to replace thenatural ball and socket structure of the joints. In total jointreplacement surgery, prosthetic ball and socket components are bothimplanted as, for example, in total hip arthroplasty wherein a femoralstem component having a head or ball thereon to replace the naturalfemoral head is affixed to the femur. A socket or acetabular componenthaving an outer shell member and a bearing insert or liner received in acavity of the shell is affixed to the acetabulum. The head or ball ofthe femoral component is rotatably or pivotally received in a socket ofthe liner to recreate the natural articulation of the hip joint. Insubtotal or partial joint replacement surgery, natural bone structure ofthe joint is left intact to cooperate with an implanted prostheticcomponent. One example of subtotal joint replacement surgery being a cuparthroplasty wherein a prosthetic acetabular or socket component isimplanted in the acetabulum to receive the natural femoral head.

It is extremely important in total or partial joint replacement surgeryand, in particular, total and subtotal hip replacement surgery, that theball and socket components be optimally positioned in accordance withthe physiological and anatomical features of the patient to ensureimplant stability, resist dislocation and subluxation of the joint,enhance range of motion and avoid loosening or failure of thecomponents. Accordingly, the liners of prosthetic acetabular componentsemployed in hip surgery have been designed to protrude beyond openingsto the cavities of the shells to angularly position the sockets of theliners to provide optimal coverage of the prosthetic femoral heads bythe socket components to resist dislocation. Many acetabular componentsincluding liners having socket openings therein and shells or cupshaving cavities therein with openings for receiving the liners withportions of the liners angularly protruding beyond the planes of thecavity openings to angularly position the socket openings to receive ahead or ball. The portions of the liners protruding beyond the planes ofthe cavity openings define angularly protruding lips or overhangs and,in some prosthetic socket components, the liners can be rotated relativeto the shells about axes perpendicular to the planes of the cavityopenings to change the position of the lips or overhangs to inhibitdislocation.

Currently available acetabular alignment apparatus and proceduresgenerally rely upon either the use of reference locations external tothe pelvis of a patient, or direct observation of an implant site by asurgeon during a prosthetic hip joint implant procedure. The relianceupon external references tends to introduce inaccuracies arising fromvariations in a patient's position on the operating room table. Thus,despite the use of elaborate and expensive equipment in connection withsuch procedures, reliable and consistent results are not assured. On theother hand, while alignment guides used by surgeons in connection withdirect observation techniques are relatively simple and inexpensive, andcan expedite the implant procedure, accuracy of alignment dependsheavily upon the skill of the surgeon and can vary widely amongpractitioners in the field.

The instrument of U.S. Pat. No. 6,395,005 provides an alignmentapparatus and method which rely upon specific anatomic structuresavailable internally at the pelvis to furnish natural landmarks asreferences for attaining accurate alignment of an acetabular device atan implant site in the pelvis. However, it is still difficult for thesurgeon to position the acetabular to prevent dislocation due toimpingement between the femoral component and the acetabular cup.

BRIEF SUMMARY OF THE INVENTION

One aspect of the present invention involves maximizing the range ofmotion in an artificial hip by ensuring the acetabular cup is installedin its optimal position with respect to the acetabulum, femoral head,and femoral neck. If the cup is installation is not optimal, impingementwill occur between the femoral neck and acetabular cup at the limits ofarticulation. Although implant trialing is a procedure that is performedto check for this fitment issue, it only offers a limited ability todetect this impingement. Since the area cannot be seen, the surgeon hasdifficulty determining when impingement occurs and must rely solely onfeel and experience. The implant trial of the present invention has theability to detect impingement and indicate its specific location. Onceimpingement is detected the surgeon can correct any misalignment easilywith an impactor. In order to sense when a hip stem impinges on anacetabular cup, three things need to be determined. The first is todetermine which components interfere and create the impingement. Thesecond is to locate the regions of contact between the components wheninstallation is not at its optimal position. Lastly, the impingementlocation needs to be communicated back to the surgeon (outside of thebody) via a simple display. This can be accomplished with a plurality ofelectric sensor contacts located around a periphery of an acetabular cuptrial. Separate wires may be connected to each contact.

One aspect of the present invention is the use of a microcontroller witha variety of small resistances and capacitive touch sensors. This allowsflexibility during testing as well as much needed room by using lesswiring compared to individually wired sensors which of course may beused. It was found that a trial cup with two-piece body design and a“softpot” (soft potentiometer) sensor (resistance touch) can fulfillthese requirements. This yields a low cost solution with a practicalapproach which can be easily manufactured. Since lower cost technologiesare used, the acetabular trial can be disposable.

The actuation of the “softpot” sensor mounted within the trial cup, onceinstalled in the body, preferably uses a plurality of flexible actuation“fingers.” The “fingers” are created in two sections, one in the trialcup body cavity, and a mating set on the rim of the trial cup Thefingers are designed to work together to prevent false signaling(“hits”) during normal femoral neck and ball articulation near theimpingement edges. A light emitting diode (LED) activation occurs whenthe neck's stem is articulated and interferes with the top corner of thetrial cup.

These aspects of the present invention can be achieved by an acetabulartrialing system having a trial acetabular cup having a body with anouter surface, a part-spherical inner surface and a rim extendingbetween the inner and outer surface. The rim includes a plurality ofspaced inwardly resiliently deflectable rim members each connected, at afirst end, to the outer surface of the body. The part-spherical innersurface has a plurality of spaced resilient deflectable bearing memberseach having an arcuate inner surface forming part of the bodypart-spherical inner surface. The bearing members have a first enddeflectable towards the body outer surface upon inward deflection. Oneof the plurality of deflectable rim members is capable of contacting thefirst end of a corresponding one of the plurality of deflectable bearingmembers and moving the bearing member towards the body outer surface. Anelectrical contact device is mounted on the body intermediate the outersurface thereof and the deflectable bearing members so that, upondeflection of the resiliently deflected bearing member towards the bodyouter surface, a surface of the bearing member contacts the electricalcontact device. The electrical contact device is capable of generating asignal when contact is made.

The trial acetabular cup electrical contact element can communicatewhich particular deflectable bearing member of the plurality ofdeflectable bearing members has made contact. Preferably the electricalcontact element is a soft membrane potentiometer extending around asubstantial portion of ortho an entire circumference of an inner surfaceof the body.

The trial acetabular trialing system further includes a control systemfor receiving input from the soft membrane potentiometer and determiningwhich deflectable bearing member is making contact therewith.

The trial acetabular trialing system further includes a display devicepreferably having a circular display capable of receiving input from thecontrol system and displaying which deflectable bearing member iscontacting the soft membrane potentiometer.

The circular clock-like display has a plurality of LED lights eachcorresponding to one of the plurality of deflectable bearing memberswherein at least one of the LED lights is activated when contact betweenthe soft membrane potentiometer and the deflectable bearing element ismade.

In one embodiment there are 12 deflectable rim elements engageable withtwelve deflectable bearing members. The deflectable bearing members formsegments of a sphere and form part of the part-spherical inner bearingsurface of the body. A surface of each deflectable bearing member facingthe body outer surface has a protrusion for contacting the electricalcontact device.

Preferably each deflectable bearing member protrusion has a rounded tipfor contacting the electrical contact element.

Each deflectable rim member has a free second end which can be deflectedinto engagement with the free first end of one of the deflectablebearing members. The first end of each rim element is molded to the bodyouter surface and the first end of the deflectable bearing member ismolded, at a polar area, to the body inner part-spherical surface.

This aspect is also achieved by a trial acetabular cup which has a bodywith an outer surface, a part-spherical inner defining cavity and a rimextending between the inner and outer surface. The rim has a pluralityof spaced inwardly resiliently deflectable rim members having a firstend connected to the outer surface and a second free end. Thepart-spherical inner surface has a plurality of spaced resilientlydeflectable bearing members. The resiliently deflectable bearing membersare spaced by slots extending from a base portion (polar area) of thecavity and having free ends adjacent the second end of the rim members.Each deflectable bearing member has an arcuate inner surface formingpart of the body part-spherical inner surface. Upon deflection of one ofthe plurality of deflectable rim members towards the body cavity the rimmember is capable of contacting a corresponding one of the plurality ofdeflectable bearing members and moving the bearing member towards thebody outer surface. An electrical contact device is mounted on the bodyintermediate the outer surface thereof and the deflectable bearingmembers so that upon deflection of the resiliently deflected bearingmember towards the body outer surface a surface of the bearing membercontacts the electrical contact element.

The electrical contact element can communicate to a user whichparticular rim member makes contact with the corresponding deflectablebearing member of the plurality of deflectable bearing members.

Upon being contacted by a deflectable bearing member the electricalcontact element can communicate to a user which particular deflectablebearing member of the plurality of deflectable bearing members has madecontact.

A control system is provided for receiving input from the soft membranepotentiometer and determining which deflectable bearing member is makingcontact therewith.

A display device preferably having a circular display capable ofreceiving input from the control system and displaying which deflectablebearing member is contacting the soft membrane potentiometer to thesurgeon.

As used herein when referring to bones or other parts of the body, theterm “proximal” means close to the heart and the term “distal” meansmore distant from the heart. The term “inferior” means toward the feetand the term “superior” means toward the head. The term “anterior” meanstoward the front part or the face and the term “posterior” means towardthe back of the body. The term “medial” means toward the midline of thebody and the term “lateral” means away from the midline of the body.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an isometric distal view of an acetabular trial cup;

FIG. 2 is the trial acetabular cup of FIG. 1 shown from the side;

FIG. 3 is a bottom view of the trial acetabular cup of FIGS. 1 and 2;

FIG. 4 is a cross-sectional view of the trial acetabular cup of FIG. 3along lines A-A;

FIG. 5 is an isometric view showing the acetabular trial cup of FIGS.1-4 including the proximal portion of a prosthetic femoral component,including a femoral head, mounted within the cup;

FIG. 6 is a cross-sectional view of the assembly of FIG. 5 showing theneck of the hip stem impinging on one of the rim elements of the trialacetabular cup;

FIG. 7 shows a control system for displaying which of the rim elementsis being contacted by the femoral neck of FIG. 6 via a light emittingdiode (LED) display;

FIG. 8 shows a kit of components comprising the acetabular trialingsystem including the trial acetabular cup of FIGS. 1-4, a trial femoralcomponent shown in part in FIGS. 5 and 6 and the controller of FIG. 7;

FIG. 9 shows an alternate embodiment of the present invention showingthe trial acetabular cup electrically connected to a clock-like displaydevice;

FIG. 10 is an enlarged view of the trial acetabular cup shown in FIG. 9;

FIG. 11 is an enlarged view of the clock-like LED display device of FIG.9 with positions 2 and 3 lit;

FIG. 12 is a bottom view of an acetabular cup trial including an outershell and an inner malleable insert capable of indicating the locationof an impingement with the neck of a prosthetic or trial femoralcomponent;

FIG. 13 is cross-sectional view of an alternate embodiment of a trialacetabular cup in which an insert may be repositioned within theacetabular cup shell by impingement with the neck of a trial or actualfemoral component which insert then remains in a fixed position when theimpingement is removed;

FIG. 14 is an isometric view showing the neck of the trial or actualfemoral component contacting the insert shown in FIG. 13; and

FIG. 15 is a cross-sectional view similar to that of FIG. 13 in whichthe neck of the prosthetic femoral component or trial femoral componentis impinging against the insert shown in FIGS. 13 and 14.

DETAILED DESCRIPTION

Referring to FIGS. 1-4, there is shown an isometric view of the trialacetabular cup of the present invention generally denoted as 10. Trialcup 10 has an outer shell 12 preferably made of polymeric material andan inner cavity 14, which has a part-spherical wall 15 with apart-spherical inner surface defined by a solid wall portion 16 adjacentthe polar region of the cavity which, upon placement in the acetabulum,is the proximal most area of the inner cavity 14. Inner cavity 14 ispreferably identical to the ultra-high molecular weight polyethylenebearing inserted in a prosthetic shell which has been implanted in theacetabulum. The inner surface of wall 15 of cavity 14 is further definedby a plurality of deflectable finger-like elements 18, which areseparated by slots 20 in wall 15 forming inner cavity 14. As can be seenin FIG. 1, there are preferably 12 finger-like deflectable elements 18separated by 12 slots 20 all forming wall 15. Also shown in FIG. 1 is arim 22 of the trial acetabular cup, which extends from an outer surfaceof shell 12 into the cavity 14. Rim 22 is composed of a plurality ofdeflectable rim elements 24 separated by slots 26, which slots extend atleast part way through rim 22. Again, in a preferred embodiment, thereare 12 deflectable rim elements 24, each corresponding to a resilientlydeflectable finger-like element 18. The trial cup 10 can either beplaced in a trial shell placed in the prepared acetabulum or preferably,in a prosthetic metal acetabular shell already implanted in a preparedacetabulum.

Also shown in FIG. 1 is a through opening 28 at the pole of the innercavity 14, which allows for reception of a manipulation instrument forpositioning trial cup 10 and can be used for fastening the trial to thealready implanted acetabular cup shell or trial shell. Also shown inFIG. 1 is electrical lead 30, which connects an electrical sensorelement mounted on a surface of the trial cup located between wall 15and outer surface 12 with a controller as will be described hereinbelow.

Referring to FIG. 2, there is shown the trial acetabular cup 10 of FIG.1 rotated in a direction toward a side view, which shows the outersurface 12 being part-spherical in shape, which would allow its beingtemporarily mounted in an inner surface of the shell located in theprepared acetabulum. For this purpose, a fastening element is insertedthrough central opening 28 of FIG. 1 into a threaded bore in the shell.Otherwise the elements shown in FIG. 2 are similar to those shown inFIG. 1. Referring to FIG. 3, there is shown a bottom view of the trialacetabular cup 10 of FIGS. 1 and 2 showing slots 20 and 26 for each ofthe 12 deflectable rim elements 24 and each of the resilientlydeflectable elements 18 aligned so that there are 12 rim elements 24each corresponding directly to one of the 12 deflectable elements of thewall inner cavity 14. For ease of use, the 12 rim elements 24 are markedwith numerals 1 through 12 so, as will be discussed below, the surgeoncan identify which rim element 24 of the trial acetabular cup is beingcontacted by the neck of a trial femoral component during a trialreduction of the joint because an LED display device uses the samenumeral for 12 lights. Note that slots 26 may extend only partly throughrim 22 leaving a bridge area 27. This is acceptable so long as each rimelement 24 can deflect inwardly towards the polar are adjacent aperture28.

Referring to FIG. 4, there is shown a cross-sectional view of the trialacetabular cup FIGS. 1-3, through lines A-A of FIG. 3. It can be seenthat cup 10 includes a body 32, preferably of a polymeric material,which body 32 is comprised of a proximal part 34 and a distal part 36.Part 36 includes rim 22. Proximal part 34 includes deflectablefinger-like elements 18 formed monolithically as part of the proximalportion 34. Since the material used to make body 32 is polymeric,elements 34 and 18 are molded, such as by injection molding, as aone-piece (monolithic) construct. Distal portion 36 likewise is moldedto include deflectable rim elements 24, which are made one-piece withthe remaining circumferential portion 37 of distal body portion 36.Portion 37 has a proximal end 39, which contacts a recessed area 40,which forms a ledge around the circumference of body portion 34. Thecontacting surface 39 and 40 may be bonded together (after electricalsensor is installed) to thereby form trial acetabular cup 10. Portion 37is integral or one piece with deflectable rim element 24 and isconnected thereto by a deflectable connector portion 38. To allow forthe deflecting of rim element 24, a cavity 42 in each distal portion 36is located between a free end 44 and the connection portion 38 of eachdeflectable rim portion 24 of distal portion 36 section 37. This allowseach deflectable rim element to deflect inwardly towards the pole ofinner cavity 14.

Also referring to FIG. 4, there is shown a circumferential softpotentiometer 46, which extends around an inner surface 48 of section 37of body portion 36. This soft potentiometer known as SoftPot may beobtained from Spectra Symbol, 3101 W. 2100 S., Salt Lake City, Utah84119. Potentiometer 46 extends almost entirely around circumferentialinner surface 48 and is connected to lead 30, which exits through a slot50 in body 32. Typically, lead 30 includes three thin copper wires 52,which connect to a controller.

Deflectable arms 18 include a protruding polymer portion 54, which cancontact soft potentiometer 46 when deflectable element 18 is movedtoward the outer surface of distal body portion 36 by member 24. As willbe discussed below, this occurs when deflectable rim portion 24 isdeflected inwardly toward the base or pole area of cavity 14 uponimpingement of the neck of a femoral component during the trialreduction. In order to facilitate the deflection of deflectable element18, a cavity 56 extends circumferentially of an outer surface 47 ofdeflectable element 18 within proximal body portion 34. As indicatedabove, both body portions 34 and 36 can be separately injection moldedand then joined after the mounting of the soft potentiometer 46 in arecessed area or a groove formed on an inner surface of outer shell 12.Soft potentiometers are well known and produce a varying resistancedepending on which deflectable element 18 is contacting thepotentiometer 46 via protrusion 54. Obviously, it is also possible tohave individual contact elements associated with each deflectableelement 18, however, this would require separate wiring to each of the12 separate electrical contact elements.

Referring to FIG. 5, there is shown a neck and head portion of a typicaltrial or actual femoral component mounted in trial acetabular cup 10. Atrial head 60 connected to a femoral component neck portion 62 ismounted within cavity 14 of cup 10 and can be rotated in any directionbecause of the part-spherical nature of both the head 60 and cavity 14.When neck 62 contacts a rim element 24 such is deflected inwardly towardthe pole of cavity 14. The free end 44 of element 24 then contactsflexible element 18 thereby moving it and its protrusion 54 into contactwith potentiometer 46. This can be best seen in FIG. 6, which shows onearea 63 of neck 62 contacting a corner 64 of rim element 24 therebydeflecting free end 44 such that a tip 66 thereof contacts an angledsurface 68 on the free end of deflectable element 18, which then movesprotrusion 54 into contact with soft potentiometer 46.

As can be seen in FIGS. 7 and 8, there is a controller generallydesignated as 100, which provides a small current to the potentiometerand can detect changes in current flow due to changes in resistancedepending on which deflectable element 18 makes contact withpotentiometer 46. Controller 100 includes 12 light-emitting diodes (LED)102, which correspond to the preferably 12 deflectable elements 18 and12 rim elements 24. Obviously fewer or more deflectable elements can beused. These LEDs are numbered in a corresponding manner to the numberson rim elements 24 so that the surgeon knows which deflectable rimelement 24 is in being contacted by the neck 62 depending on which lightis illuminated. If two elements light up simultaneously, the surgeonknows that the neck is impinging at a point intermediate the twonumbered deflectable rim elements. Referring to FIG. 8, there is shownthe entire acetabular trialing system, including cup 10, control box100, and femoral trial component with neck 62 and head 60, including astem 65. As shown in FIG. 8, stem 65 may be part of a broach or raspused to prepare the femoral canal.

The wire between the trial cup and the LED display clock would extendout of the wound. The LED clock would be visible as a trial reduction isperformed. A trial range of motion (ROM) is performed, LED lights light,then surgeon determines if he want to adjust cup in a way that would besuch that would avoid the LED light from lighting. The operation wouldbe re-performed until the surgeon is satisfied with the patient ROM andeither the lack of impingement (LED light lighting up), or that the legROM is acceptable even though there is identified impingement.

Another important aspect of this invention is that the impingement isidentified after the femoral stem is placed in the femur. It takes intoaccount the actual position of the femoral stem (trial stem or actualimplant) which is important as the stem neck does not always recreatethe natural body bony femoral neck anatomy. Also, that currently whendoing a trial ROM, the surgeon may detect that there is ROM resistancedue to impingement, but he currently does not know if it is due to theneck of the stem impinging on the edge of the trial (or actual implant)or is it due to bony impingement, or soft tissue impingement/resistance.This invention addresses this since if the trail cup is contacted an LEDlights.

Referring to FIG. 9, there is shown a trial acetabular cup 100 connectedto a clock-like device 102 which includes 12 LED lights 104. The lights104 are connected to trial acetabular cup 100 by a cable 106. As shownin FIG. 9, the display device 102 includes 12 LEDs 104.

Referring to FIG. 10, there is shown an enlarged view of acetabulartrial cup 100 which includes 12 resiliently deflectable contact elements108 which contact electrical sensors 110 mounted on a rim 112 of cup100. As can be seen in FIG. 10, there are 12 positions spaced at 30°intervals around the 360° circumference around inner surface 114 of rim112. Each electrical contact sensor 112 is connected via a dedicatedwire which feeds cable 106. The 12 wires carry electrical signals to theLEDs 104 on display 102. Electrical contact elements 108 may be mountedon a resiliently deflectable polymeric ring 116 which can deflectoutwardly towards surface 114 of rim 112 when contacted by a femoralcomponent neck. Upon this outward deflection, contact element 108contacts sensor 110 to produce the signal. Since there are 12 individualwires each connected to a sensor 110, the signal generated will indicatewhich area of the rim circumference is making contact with the neck. Ofcourse, if no impingement occurs between the trial cup and the femoralcomponent stem, no light will be lit.

Referring to FIG. 11 there is an enlarged view of the clock-like display102 shown in FIG. 9. As can be seen, there are 12 LEDs 104 correspondingto the 12 positions on cup 110. These LEDs are connected by wires to theelectrical contact sensors 110 by cable 106. Cable 106 also carries aninput current which powers the lights when contact between elements 108and sensor 110 occur. As can be seen in FIG. 11, LEDs 2 and 3, labeled105, are lit which would occur when the neck of the femoral componentimpinges the area of rim 116 between numerals 2 and 3 of trial cup 100.

In the use of either embodiment 10 or 100 of acetabular cup trial, theacetabulum is first prepared by reaming and the femur is prepared by,for example, broaching. A trial shell or actual prosthetic shell implantis press-fit into the reamed acetabular socket. The disposable inserttrial cup 10, 100 is then placed therein with the electrical cableextending outside of the wound. A femoral component is then placed inthe broached femur with a head and neck trial placed thereon and thejoint is reduced by the surgeon. The surgeon then conducts a trial rangeof motion test to see which lights, if any, light on the display deviceto indicate impingement with the LEDs being lit designating where theimpingement occurs. If unacceptable impingement occurs, the femoralcomponent and head is distracted from the trial cup 10, 100 and theacetabular shell is repositioned in the acetabulum as needed. The rangeof motion test is repeated until the surgeon is satisfied with the shellposition. The surgeon then marks the bone location for the shell sothat, if a trial shell was used, the prosthetic shell can be located inthe correct position. Of course if the actual prosthetic acetabularshell was used during the test, then this step can be eliminated.

It is also possible to use, instead of or in addition to lights, theelectrical contact to trigger a sound, like a ring or buzz as an audibleinduction of impingement. It is also possible to have a controller whichonce the lights are lit they stay on after the electrical connection isbroken. This would allow the user to see which region had contactwithout having to recall which lights had been on. A reset button wouldturn off the lights.

Rather than have the indicator of impingement of the implant or trialneck on the trial shell be a light or sound triggered by electricalcontact, the indicator could simply be a deformation of a malleableportion of the trial insert for example around the rim. For example,clay would have sufficient mechanical integrity to be placed into theoperative site but would also be deformed if it came into contact with aneck during a range of motion determination. A metal or polymer materialwould also be suitable if it had similar mechanical properties. Anydeformation to the malleable rim that occurs during reduction of thetrial (i.e. placing the femoral head (trial or implant) into the trialinsert should be avoided, but if it does occur it will be different inappearance to the type of deformation caused by impingement of thefemoral component neck (trial or implant) on the malleable rim.

After placement of the malleable trial insert into either an implant ortrial shell and subsequent range of motion testing of the trial joint,any place where the neck impinged on the malleable trial insert rimwould be readily apparent. The shell could then be repositioned based onthat information. This step could be performed multiple times initerative fashion if deemed necessary by the surgeon with eachsubsequent adjustment moving the shell closer to the optimal position.If multiple iterations are necessary, the same malleable trial insertmay be able to be used each time, but the surgeon may also choose to usea new malleable trial insert for each iteration since the new trialinsert will not have any deformed spots on the rim from previousiterations. Such an implant is shown in FIG. 12 in which there is showna trial acetabular cup generally denoted as 150 having a cavity 151. Thecup includes a metal shell 153 having an inner rim area 155 with amalleable insert 154 located around the circumference of the innercavity 151 at least in the area of the rim 155. When the trial or actualfemoral component neck impinges on the malleable element 154 adepression 160 is formed thereon. Anti-rotation elements 158 areprovided to ensure that the malleable insert 154 does not rotate withrespect to shell 153 when the femoral component neck makes contacttherewith.

Another possibility is rather than having the rim of the trial insertdeform when the neck makes contact, the entire insert could rotate inthe shell. Friction between the insert and shell would serve to hold theinsert in its new position once the rotation had occurred. The frictioncould be provided and controlled by a center post component that isthreaded into the shell and captures the trial insert in the shellwithout fixing the trial insert in one angular orientation. The threadedapical holes on many commercially available acetabular implants andtrials such as Trident® cup system by Stryker Corp. used to aidinsertion of the components could easily accommodate the center postcomponent.

The rotatable trial insert would preferably be initially aligned withthe shell into which it is placed in that the face (equator) of thetrial insert would be parallel to the face (equator) of the shell andheld there by friction. After trial reduction of the joint followed byrange of motion testing, the face of the rotatable insert may be movedinto a position that is no longer parallel to the face of the shell. Theposition of the face of the insert could then serve as a guide to theproper orientation of the face of the shell that will maximize range ofmotion of the joint and minimize the potential for impingement of thefemoral neck implant and acetabular shell implant. Such a rotatableinsert is shown in FIGS. 13-15 and is generally denoted as 200.Referring to FIG. 13 there is shown the trial or actual femoralcomponent 190 including a neck section 192 and a conically taperedtrunnion 194. The conically tapered trunnion 194 mates with a conicallytapered female bore 196 of a prosthetic femoral head 198.

The trial acetabular cup 200 includes an outer shell 202 with apart-spherical inner surface 203 in which an insert 204 is mounted.Insert 204 has a part-spherical outer surface 206 which can rotate onsurface 203. Cup 202 includes a polar region with a bore 208 whichincludes threads 210. Threaded bore 208 in turn receives a center post212 which has a flange portion 214 capable of sliding in all directionswithin a groove 216 formed within the polar area of insert 204. Post 212produces sufficient force between surfaces 203 and 206 to develop africtional force which maintains cup 204 in a position within shell 202even after relative rotation therebetween.

Referring to FIGS. 14 and 15 this situation is shown when the neck 192of femoral component 190 contacts surface 218 as shown in FIG. 15. Thiscontact causes insert 204 to be rotated for example to a positionwherein an end 220 of post 212 contacts surface 224 of recessed area 216within insert 204. Because of the friction produced between surfaces 203and 206, by a surface 226 of post 212 contacting surface 228 of shellrecess 216, the insert 204 remains in the position produced by theimpingement of neck 192 against surface 218 even after the femoralcomponent 190 is moved to a position in which the neck 192 is no longerimpinging against insert 204.

Although the invention herein has been described with reference toparticular embodiments, it is to be understood that these embodimentsare merely illustrative of the principles and applications of thepresent invention. It is therefore to be understood that numerousmodifications may be made to the illustrative embodiments and that otherarrangements may be devised without departing from the spirit and scopeof the present invention as defined by the appended claims.

The invention claimed is:
 1. An acetabular cup trialing systemcomprising: a body having a spherical inner cavity surrounded by acircumferential rim; an electrically conductive contact sensor connectedto a power source located on the circumferential rim, the contact sensorextending around a circumference of the rim and capable of producing anelectrical signal when contacted, the electrical signal varyingdepending on the location along the contact sensor; and a plurality ofresiliently deflectable contact elements spaced around the circumferenceof the rim and spaced radially inwardly of the contact sensor towardsthe inner cavity, an outward deflection of the deflectable contactelement is configured to move the element into contact with the contactsensor to produce the electrical signal; and a display device connectedto the contact sensors for indicating which of the deflectable contactelements has been deflected.
 2. The acetabular trialing system as setforth in claim 1 wherein there are twelve resiliently deflectablecontact elements spaced at 30 degree intervals around the circumferenceof the rim.
 3. The acetabular trialing system as set forth in claim 2further comprising a control system associated with the display devicefor receiving input from the contact sensor and determining whichdeflectable bearing member is making contact therewith.
 4. Theacetabular trialing system as set forth in claim 3 wherein the contactsensor is a soft membrane potentiometer and the display device has acircular display capable of receiving input from the control system anddisplaying which deflectable bearing member is contacting the softmembrane potentiometer.
 5. An acetabular cup trialing system comprising:a trial acetabular cup having a body comprising an outer surface, apart-spherical inner surface and a rim extending between the inner andouter surface, the rim comprising a plurality of spaced resilientlydeflectable rim members each connected at a first end to the body outersurface, the part-spherical inner surface comprising a plurality ofspaced resiliently deflectable bearing members each having an arcuateinner surface forming part of the body part-spherical inner surface, thedeflectable bearing members having a first end deflectable towards thebody outer surface; upon deflection, one of the plurality of deflectablerim members is capable of contacting the first end of a correspondingone of the plurality of deflectable bearing members and moving thebearing member towards the body outer surface; and an electrical contactsensing device connected to a power source mounted on the bodyintermediate the outer surface thereof and the deflectable bearingmember, the deflectable bearing members are configured to contact theelectric contact sensing device upon deflection towards the body outersurface, the contact sensing device having a variable output dependingon which of the bearing members contact the electrical contact sensingdevice.
 6. The acetabular trialing system as set forth in claim 5wherein the electrical contact device communicates which particulardeflectable bearing member of the plurality of deflectable bearingmembers has made contact.
 7. The acetabular trialing system as set forthin claim 6 wherein the electrical contact element is a soft membranepotentiometer extending around an entire circumference of an innersurface of the body.
 8. The acetabular trialing system as set forth inclaim 7 further comprising a control system for receiving input from thesoft membrane potentiometer and determining which deflectable bearingmember is making contact therewith.
 9. The acetabular trialing system asset forth in claim 8 further comprising a display device having acircular display capable of receiving input from the control system anddisplaying which deflectable bearing member is contacting the softmembrane potentiometer.
 10. The acetabular trialing system as set forthin claim 9 wherein the circular display comprises a plurality of lightemitting diode (LED) lights each corresponding to one of the pluralityof deflectable bearing members wherein at least one of the LED lights isactivated when contact between the soft membrane potentiometer and thedeflectable bearing element is made.
 11. The acetabular trialing systemas set forth in claim 5 wherein the electrical contact element is acontinuous soft membrane potentiometer extending around an innercircumference of the trial acetabular cup body.
 12. The acetabulartrialing system as set forth in claim 5 wherein there are 12deflectablerim elements engageable with twelve deflectable bearing members.
 13. Theacetabular trialing system as set forth in claim 12 wherein these12deflectable rim and bearing members.
 14. The acetabular trialingsystem as set forth in claim 5 wherein the deflectable bearing membersform segments of a sphere and form part of the part-spherical bearingsurface of the body.
 15. The acetabular trialing system as set forth inclaim 5 wherein a surface of each deflectable bearing member facing theouter surface has a protrusion for contacting the electrical contactmember.
 16. The acetabular trialing system of claim 15 wherein eachdeflectable bearing member protrusion has a rounded tip for contactingthe electrical contact element.
 17. The acetabular trialing system asset forth in claim 5 wherein each deflectable rim member has a secondfree end which can be deflected into engagement with the first end ofone of the deflectable bearing members.
 18. A acetabular trialing systemcomprising: a hip femoral component; a trial acetabular cup having abody comprising an outer surface, a part-spherical inner defining cavityand a rim extending between the inner and outer surface, the rimcomprising a plurality of spaced resiliently deflectable rim membershaving a first end connected to the body and a second free end, thepart-spherical inner surface comprising a plurality of spacedresiliently deflectable bearing members, the resiliently deflectablebearing members spaced by slots extending from a base portion of thecavity and having free ends adjacent the second end of the rim members,each bearing member having an arcuate inner surface forming part of thebody part-spherical inner surface, the plurality of deflectable rimmembers are deflectable towards the body inner cavity by contact withthe femoral component, upon deflection rim members are capable ofcontacting one of the plurality of deflectable bearing members andmoving the bearing member towards the body outer surface; and anelectrical contact sensing element connected to a power source mountedon the body intermediate the outer surface thereof and the deflectablebearing member, deflection of the resiliently deflected bearing membertowards the body outer surface by the femoral component contact with thedeflectable rim-member is configured to cause a surface of the bearingmember to contacts the electrical contact sensing element.
 19. Theacetabular trialing system as set forth in claim 18 wherein theelectrical contact element communicates to a user which particulardeflectable bearing member of the plurality of deflectable bearingmembers has made contact.
 20. The acetabular trialing system as setforth in claim 19 further comprising a control system for receivinginput from the soft membrane potentiometer and determining whichdeflectable bearing member is making contact therewith.
 21. Theacetabular trialing system as set forth in claim 20 further comprising adisplay device having a circular display capable of receiving input fromthe control system and displaying which deflectable bearing member iscontacting the soft membrane potentiometer.
 22. The acetabular trialingsystem as set forth in claim 19 wherein the electrical contact elementis a continuous soft membrane potentiometer extending around an innercircumference of the trial acetabular cup body.
 23. The acetabulartrialing system as set forth in claim 18 wherein there are 15deflectablerim elements engageable with twelve deflectable bearing members.
 24. Theacetabular trialing system as set forth in claim 18 wherein thedeflectable bearing members form segments of a sphere and form part ofthe part-spherical bearing surface of the body.